feat(sidekick/swift): bootstrap method generation (#5146)

Generate a skeleton of each method, the skeleton just crashes the
application (think `assert()`) for now. It should have the correct
return type for the APIs we want to generate, but does not support
`google.protobuf.Empty`, or pagination, or LROs yet.

Author: coryan

internal/sidekick/swift/annotate_method.go

@@ -0,0 +1,33 @@
+// Copyright 2026 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package swift
+
+import (
+	"github.com/googleapis/librarian/internal/sidekick/api"
+)
+
+type methodAnnotations struct {
+	Name     string
+	DocLines []string
+}
+
+func (codec *codec) annotateMethod(method *api.Method) {
+	docLines := codec.formatDocumentation(method.Documentation)
+	annotations := &methodAnnotations{
+		Name:     camelCase(method.Name),
+		DocLines: docLines,
+	}
+	method.Codec = annotations
+}

internal/sidekick/swift/annotate_method_test.go

@@ -0,0 +1,86 @@
+// Copyright 2026 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package swift
+
+import (
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+	"github.com/googleapis/librarian/internal/sidekick/api"
+)
+
+func TestAnnotateMethod(t *testing.T) {
+	method := &api.Method{
+		Name:          "CreateSecret",
+		Documentation: "Creates a secret.",
+	}
+	service := &api.Service{
+		Name:    "SecretManagerService",
+		Methods: []*api.Method{method},
+	}
+	model := api.NewTestAPI(nil, nil, []*api.Service{service})
+	codec := newTestCodec(t, model, nil)
+
+	if err := codec.annotateModel(); err != nil {
+		t.Fatal(err)
+	}
+
+	want := &methodAnnotations{
+		Name:     "createSecret",
+		DocLines: []string{"Creates a secret."},
+	}
+
+	if diff := cmp.Diff(want, method.Codec); diff != "" {
+		t.Errorf("mismatch (-want +got):\n%s", diff)
+	}
+}
+
+func TestAnnotateMethod_EscapedName(t *testing.T) {
+	for _, test := range []struct {
+		name       string
+		methodName string
+		wantName   string
+	}{
+		{"escaped func", "Func", "`func`"},
+		{"escaped self", "Self", "self_"},
+		{"escaped default", "Default", "`default`"},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			method := &api.Method{
+				Name:          test.methodName,
+				Documentation: "Test documentation.",
+			}
+			service := &api.Service{
+				Name:    "TestService",
+				Methods: []*api.Method{method},
+			}
+			model := api.NewTestAPI(nil, nil, []*api.Service{service})
+			codec := newTestCodec(t, model, nil)
+
+			if err := codec.annotateModel(); err != nil {
+				t.Fatal(err)
+			}
+
+			want := &methodAnnotations{
+				Name:     test.wantName,
+				DocLines: []string{"Test documentation."},
+			}
+
+			if diff := cmp.Diff(want, method.Codec); diff != "" {
+				t.Errorf("mismatch (-want +got):\n%s", diff)
+			}
+		})
+	}
+}

internal/sidekick/swift/annotate_service.go

@@ -35,4 +35,7 @@ func (codec *codec) annotateService(service *api.Service, model *modelAnnotation
 	}
 
 	service.Codec = annotations
+	for _, method := range service.Methods {
+		codec.annotateMethod(method)
+	}
 }

internal/sidekick/swift/templates/common/service.swift.mustache

@@ -26,5 +26,16 @@ import Foundation
 /// {{{.}}}
 {{/Codec.DocLines}}
 public class {{Codec.Name}} {
-  {{! TODO(#....) - add method generation }}
+  {{#Methods}}
+
+  {{#Codec.DocLines}}
+  /// {{{.}}}
+  {{/Codec.DocLines}}
+  public func {{Codec.Name}}(request: {{InputType.Codec.Name}}) async throws
+    {{! TODO(#5138) - deal with `google.proto.Empty` and other complex return types }}
+    -> {{OutputType.Codec.Name}}
+  {
+    fatalError("Unimplemented")
+  }
+  {{/Methods}}
 }